The present invention relates to electrical circuit test probes and electrical connectors therefor and, more particularly, to an electrical circuit test probe with a spring loaded plunger in a socket tube having an offset wand extending therefrom to contact the interior of a member disposed within the socket tube and wherein the socket tube is provided with a releasable connector for a conductor comprising a plug housing formed in the end of the socket tube and a collet jawed plug for gripping the electrical conductor and slidably fitting within the plug housing to grip the conductor and hold it therein in electrical contact.
Of necessity, electrical circuit testing has made rapid strides in its technology in the past few years. Until the advent of miniaturization, circuit testing, took the form shown in FIG. 1. To test whether a large fuse 10 was electrically conductive, a pair of large, hand-held probes 12 connected to a meter 14 were placed across the fuse 10.
Modern printed circuit (PC) boards have made such hand testing virtually impossible. Literally hundreds of connections at close-spaced proximity must be tested to verify proper circuit continuity. To do this in an automated way, apparatus such as that shown in FIG. 2 has come into common usage. The PC board 16 is positioned on a holding table 18 and a fixture 20 having a plurality of electrical test probes 22 is brought into contact with the surface thereof. The probes 22 are connected by cable 24 to testing logic 26. In this manner, the testing logic 26 can quickly and accurately test a multitude of circuit interconnections for proper continuity.
As can be readily understood, the functioning of the probes 22 relative to the fixture 20 and their electrical connection to the testing logic 26 are critical to the successful operation of the testing apparatus. Any failure of the probe 22 to make effective electrical contact with the PC board 16 or any failure of the electrical contact so made to be effectively passed back to the testing logic 26 will be interpreted, wrongfully, by the testing logic 26 as a failure of the PC board 16.
Two aspects are critical in the overall operation of the probes 22. First, the probes 22 must have a degree of linear axial movement within the fixture 20 to accommodate variations in projection of contact points from the PC board, thereby to prevent undue pressure on the PC board 16 and/or breakage of the probe 22 while ensuring adequate electrical contact. Second, is the manner of electrically connecting a conductor from the cable 24 to the probe 22. Some of these aspects according to the prior art are shown in FIGS. 3-8.
Turning first to FIG. 3, a probe is shown according to U.S. Pat. No. 4,200,351. The probe, generally indicated as 28, comprises a spring-metal tube 30 press-fit within bore 32 of fixture 20. Probe 28 has a first cylindrical portion 34 adapted to slidably fit within the tube 30 and having a head 36 on the outer end thereof for contacting the PC board 16. A smaller diameter cylindrical shaft 38 extends from the cylindrical portion 34 in axial alignment therewith to pass through the bore 32 and terminate in an end 40 having a square cross-section particularly adapted for attachment of an electrical conductor thereto by a so-called Wire Wrap process. An enlarged portion 42 on the shaft 38 contacts the outer ends of fingers 44 formed into the tube 30 to prevent longitudinal movement out of the tube 30 of the head 36 beyond a pre-established maximum point. A spring 46 is under compression between shoulder 48 and the inside of the fingers 44 to bias the assembly to its outer position. Since the electrical connection to the probe (not shown) is directly attached to the end 40, there is no danger of loss of electrical continuity as the probe 28 is moved in and out of bore 32. On the negative side, should it be desired to reconfigure the probe 28 or replace it, the task is not a simple one.
A test probe of the type shown in U.S. Pat. No. 4,168,873 is shown in FIG. 4 and generally indicated at 50. Probe 50 comprises a socket tube 52 which is slid into a pair of aligned bores 32 in the fixture 20. Electrical connection is provided to the tube 52 by pressing the electrical conductor 54 into a pair of jaws 56 in connector member 58, which is crimped into the one end of the socket tube 52. A tubular sleeve 60 is fitted into the end of the socket tube 52 adjacent the connector member 58. The head 36 is mounted on a shaft 62 having a cylindrical portion 64 sized to slidably fit within the tube 52. Correspondingly, the inner end of the shaft 62 is sized to slidably fit within the tubular sleeve 60. Spring 46 is disposed between the tubular sleeve 60 and the cylindrical portion 64 to provide the outward biasing force on the head 36. Stop member 66 is provided to prevent the shaft 62 from moving outward past its previously selected maximum point. With this embodiment, the socket tube 52 can be easily removed from the bores 32 as necessary. To release the electrical conductor 54, however, it must be pried from between the jaws 56. Electrical contact between the moving shaft 62 and the electrical conductor 54 is hoped for by contact between the cylindrical portion 64 and the inside of the socket tube 52 in combination with contact between the inner end of the shaft 62 and the inside of the tubular sleeve 60.
Turning now to FIG. 5, a probe, generally indicated as 68, is shown according to the teachings of U.S. Pat. No. 4,461,993. In this particular case, a tube 70 is mounted within the bore 32 of fixture 20. The head 36 comprises the end of a cylindrical shaft 72 slidably mounted within a tube 74 having its opposite end 76 of a reduced diameter adapted to snugly fit within the tube 70. The electrical conductor (not shown) is electrically connected to the tube 70 in any manner desired and electrical connection is made between the tubes 70, 74 by their snug fit together in electrical contact. Shaft 72 has a reduced diameter portion 78 and a bulbous end 80. The tube 74 is crimped as at 82 to prevent the shaft 72 from moving out of tube 74 beyond its desired extension limit. A spring 46 is positioned within the tube 74 between the portion 78 and the bulbous end 80 to urge the head 36 to its extended position. While tube 74 and its assembled components can be easily removed from the tube 70 without disconnection of the electrical conductor (not shown), once again, electrical connection between the tube 74 and shaft 72 is hoped for by the sliding contact of the shaft 72 on the inside of tube 74, sliding contact of the bulbous end 80 within tube 74, and electrical contact by the spring 46 between the tube 74 and end 80.
The prior art configurations of FIGS. 6-8 are variations that can be applied to the embodiments of FIGS. 4 and 5 in an attempt to provide a greater probability that electrical contact will be provided between the outer tube and the shaft sliding therein containing the head 36. FIG. 6 corresponds to the teaching from U.S. Pat. No. 4,050,762. In this case, a spring member 82 having fingers 84 is mounted to the end of the moving shaft 86 to press against the inside walls of the tube 88.
FIG. 7 shows the teachings of U.S. Pat. No. 3,753,103, wherein a contact member 90 is connected to the end of sliding shaft 92 by a leaf spring 94 providing a biasing couple tending to urge the contact member 90 against the inside walls of the tube 96.
Finally, in FIG. 8, which corresponds to U.S. Pat. No. 4,397,519, the inner end 98 of shaft 100 is angled at surface 102 and the biasing force of the spring 46 is applied through a ball 104 against angled surface 102 which results in a biasing force vector from spring 46 also being provided against end 98 towards the inner side wall of the tube 105.
All the above-described prior art probes, many of which remain mere paper proposals, and their manner of connection to the electrical conductor connected thereto have one or more problems relating to mechanical and electrical effectiveness and reliability, and cost, ease of manufacture and ease of use. Especially as the center-to-center spacing between probes in a multi-probe fixture of necessity becomes smaller and smaller as boards to be tested become corespondingly smaller, there is a requirement for a probe which is simple to manufacture because of few and simple parts, while, at the same time, being easily replaceable and completely reliable in its electrical conductivity.
Wherefore, it is the object of the present invention to provide an electrical circuit test probe and connector combining these features.